Washington -LRB- CNN -RRB- -- As President Obama is set to take stock of the nation during his State of the Union address Tuesday , a civil engineers group gives the U.S. transportation system low grades .

For example , the nation 's bridges . Most of us do n't think much about bridges until one we need is closed or is damaged or collapses , as the I-35W one did in Minneapolis in 2007 , killing 13 people .

Yet engineers all over the country who really know about such things say we ought to be thinking about bridges a lot more .

And here is something we should consider : One in four of our bridges is either in need of repair or obsolete in terms of handling modern traffic and loads .

That startling fact comes from the American Society of Civil Engineers , which every few years consults with dozens of the nation 's experts on all sorts of infrastructure matters . The society gives U.S. bridges a grade of C.

And bridges are n't the only problem in what we could call the State of the Union 's Infrastructure . Roads , airports , water supplies , railways , dams , schools and on and on it goes ; all are , according to the engineers ' latest report in 2009 , in pretty dire shape .

The amount of air travel in the U.S. increased by 7 % last year , but an overhaul of the air travel infrastructure is long overdue , according to the American Society of Civil Engineers . The group gave the nation 's aviation system a grade of D. Compared with trucks , railways are much more efficient for moving goods : using about 20 % less energy per mile if used properly . But comparatively little has been invested in expanding U.S. railroad capacity . Rail gets a C minus . What is the state of your community ? Tell us

Consider this : Although a steady drinking water supply is crucial to even the most basic success , water systems nationwide are so old and decrepit that the American Society of Civil Engineers estimates 7 billion gallons of drinking water are being lost through leaky pipes every day .

How can America save crumbling water delivery systems ?

Inland shipping along canals and rivers keeps millions of American homes warm with coal and families fed with grains such as wheat and corn . But locks on canals and rivers , which were made to last only 50 years , are now on average 60 years old . Navigable waterways get a D minus from the civil engineers . See details of the ASCE report card

Public transit use grew 25 percent in the past 10 years , and yet fully half of all Americans have no access to commuter buses or trains ; many more have sketchy access at best . You get the picture . However , it may be a little harder to see the multiplying effect .

Experts at the American Society of Civil Engineers point out that for each year that these infrastructure problems are not addressed , they grow exponentially worse .

It 's kind of like a leak in the roof . It may be painful to pay for new shingles when the leak is small , but if you wait until it expands and soaks the walls and floors below , the damage and cost will be much , much harder to bear .

In recent years , many politicians have started talking much more seriously about infrastructure problems , but when faced with a stumbling economy , they are finding it harder than ever before to lean into big-ticket repairs . After all , until the day comes that a bridge falls down , it often looks just fine .

The problem is , no one really knows which day that will be .

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Society of civil engineers gives U.S. low grades for transportation infrastructure

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Air travel infrastructure overhaul is long overdue , while traffic increased by 7 % last year

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Half of all Americans have no access to commuter buses or trains

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The longer these problems go unaddressed , the worse they grow